The invention relates to a method and an apparatus for desorption of a blood sample from a medical test sheet comprising at least one dried blood spot thereon, for the purpose of biomedical analysis of the blood sample.
Such a medical test sheet may for example comprise filter paper and/or other suitable material for containing the at least one dried blood sample thereon. A widely used such medical test sheet is for example the filter paper Whatman 903®, which filter paper has a thickness of about 0.5 millimeter. Five lined-up circles are preprinted on one face of such a Whatman 903® filter paper. These circles each have a diameter of about 12 millimeter. One or more drops of blood can be placed within these circles. After drying, the filter paper thus comprises at least one dried blood spot thereon.
In order to analyse such a dried blood spot, at first, compounds need to be extracted from the filter paper. For that purpose, according to usual practice, a disc area corresponding to a preprinted circle on the filter paper containing dried blood sample, or of smaller diameter than that of the preprinted circle, is punched out of the filter paper.
Traditionally, the punched-out disc is then placed into a little tray, bottle, other container, or the like. The extraction procedure is then carried out by an organic solvent or a mixture of water thereof, containing an internal standard (IS). Traditionally, after extraction and centrifugation, the supernatant is collected and analysed by liquid chromatography mass spectrometry.
More recently, another concept has been described in the article Julien Déglon, Aurélien Thomas, Antonio Cataldo, Patrice Mangin, Christian Staub, “On-line desorption of dried blood spot: A novel approach for the direct LC/MS analysis of μ-whole blood samples”, Journal of Pharmaceutical and Biomedical Analysis 49(2009) 1034-1039. Said article presents a new concept allowing the direct analysis of a dried blood spot coupled to a liquid chromatography mass spectrometry device (LC/MS). According to this new concept, a 10 millimeter disc containing dried blood sample is punched out of the filter paper sheet and an IS solution is added directly on the dried blood sample. Then, the blood disc is placed into a desorption cell, which is an inox cell that comprises two parts which can be brought in sealing engagement with each other via a separate sealing ring. The separate sealing ring has external-internal diameters of 14 and 12 millimeter, respectively, and thickness of 1.5 millimeter. The cell is then integrated into an LC/MS system where the analytes are desorbed out of the paper towards a column switching system ensuring the purification and separation of the compounds before their detection on a single quadrupole MS coupled to atmospheric pressure chemical ionisation (APCI) source. This new concept presented in said article is called “on-line” desorption of dried blood spots (“on-line DBS”), to indicate its distinction from the above-described traditional “off-line” extraction, in which compounds need to be extracted from the filter paper disc prior to analysis.